Dispensers of the aforementioned type are known for example from US-A1-2003/0169046 and U.S. Pat. Nos. 6,695,246 B1 and 6,069,354.
In for example the dispenser according to U.S. Pat. No. 6,695,246 B1, the sensor control circuitry uses either passive infrared (IR), i.e. detection of reflected ambient IR, or active IR (both IR emission and detection) to control sensing of the presence of a possible user. In the active IR mode the presence of an object (i.e. a possible user) can be detected within a detection zone of about 12 to 24 cm from the dispenser and upon said detection operates a motor to dispense a hand towel to a user. The detection zone is kept small so that objects which are outside the detection zone do not lead to undesired and unintentional dispensing. When in the desired zone, the microprocessor controlling the motor operation only activates the motor to dispense a towel when two scans are received by the IR sensing circuitry. The microprocessor can be operated to scan at about 7 Hz (i.e. 1 scan each 0.14 seconds) by using an oscillator to turn power to the microprocessor on and off. Alternatively, it can be set to operate at a different frequency. When the motor is operating the microprocessor is kept on constantly.
US-A1-2003/0169046 discloses a dispenser in which an IR sensing system is mentioned as an alternative to capacitance detection for proximity detection. In an example of capacitance-type sensing the capacitative type sensor is connected to a microprocessor. No details are given as to where an IR sensing system, if present, would be located, nor how it would be arranged to operate. A further sensor system is included for detecting paper web in a discharge chute. This further sensor system for the paper uses the microprocessor to pulse power on/off to optical sensors. Additionally, a watch-dog timer can be used which closes down the pulsing function and resumes it again when it periodically wakes the microprocessor from sleep mode.
U.S. Pat. No. 6,069,354 discloses a dispenser using active IR which generates a square wave at about 1.2 kHz so as to emit a modulated IR signal, which is detected by reflection against a possible user to an IR detector. This document proposes using a sensor system set to sense a user between about 1.25 cm and about 30 cm distant from the dispenser.
The aforementioned documents all use sensor systems which, when active, operate at a specific scanning rate (frequency) to operate a motor to dispense a piece of towel.
The aforementioned dispensers operate by using a scanning rate (number of scan per second), which is fixed when the device is active. This rate is kept fairly high so that when a user is in a detection zone, the dispenser will not take too long to dispense. This high scanning rate means however that power is being consumed at a high level since the IR emitters and detectors need to be activated very often and these consume power when active. Using a lower scanning rate would of course save power, but the time to dispense a towel would then be longer, and when the user moves his/her hands towards the dispenser rapidly after washing, this can give the impression to the user that the device is not detecting him/her properly if a towel is not dispensed immediately.
The present invention has as one of its objects, the provision of low power consumption by the sensor system in periods when a possible/potential user (i.e. an object assumed to be a user requiring dispensing of a product such as a length of hand towel or toilet paper) is not located near enough to the dispenser, and at the same time to provide a relatively quick reaction time when a possible/potential user is near enough to the dispenser and needs a towel to be dispensed. Low power consumption is particularly important in dispensers which are entirely battery powered by one or more replaceable batteries, especially those battery systems that operate without a recharging possibility by a solar cell recharging system or other type of recharging system, as dispensers of this type are generally expected to operate for a long time (e.g. enough time to dispense 60 or more rolls of paper without requiring battery replacement).
A further object of the invention is to allow still further power saving when there are no possible users in the vicinity of the dispenser.
Still further objects of the invention will be apparent on reading this specification.